1. Field of the Invention
The invention relates to the field of video displays and in particular, the processing of data to generate video signals.
2. Prior Art
There are numerous commercial systems and many others described in printed publications for providing an interface between a digital computer and a raster scanned video display. The conversion of the computer's digital information into the pixel data used by a conventional raster scanned CRT requires considerable data manipulation, particularly for a complex color graphics. In many personal computers a substantial portion of the microprocessor's time is spent manipulating data just for this purpose, since an enormous amount of data is typically moved to generate each frame. The enormity of the problem can be appreciated by the fact that with current techniques, to produce a graphics display having the quality of, for example, a 35 mm film, requires computational power far beyond that of current microprocessors and indeed, beyond that of many mini-computers and mainframe computers for reasonable interactive performance.
There has been a great deal of emphasis on developing circuitry which will provide enhanced displays, through use of special purpose circuitry, "graphics engines" and the like without placing additional burdens on the computer's CPU. The present invention falls into this category in that it provides a graphics engine which, while operating under the general control of a CPU, generates the pixel data substantially independent of the CPU.
In many current graphics systems a bit map memory (e.g., frame buffer) is used to store the pixel data before the data is displayed. The data within these memories is moved for each frame often under the control of the CPU. In some cases, the pixel data is composed within the frame buffer and, for example, data may be written into the same locations several times to obtain the final pixel data. A typical frame buffer is described in conjunction with FIG. 2b, and the difference between this prior art storage technique and the present invention is described in conjunction with FIG. 2c.
In general, the present invention provides an improved graphics display by relying upon additional memory capacity rather than processing speed. It is believed that with the continuing decline in memory costs, this approach is considerably more economical than relying upon increased processing speed. Indeed, over the last few years the cost of storage in terms of cents per bit has decreased at a far greater rate than the speed of microprocessors or the cost of obtaining faster processing.